1. Field of the Invention
The present invention relates to computer systems which are performance upgrades of other computer systems. More specifically, the invention relates to computer systems in which one or more important elements, such as the central processing unit, of a known computer system are replaced with elements having higher performance characteristics.
2. Related Art
It is known in the art that given computer systems may be upgraded in performance through substitution of elements. The new elements have higher performance capabilities than elements in the original system.
For example, in the field of personal computers, the IBM.RTM. AT.RTM. computer (available from International Business Machines Corporation, Armonk, N.Y.) is known. This known computer operates using an 80286 processor and an 80287 math coprocessor available from, for example, INTEL Inc. of Santa Clara, Calif. Other manufacturers have since designed computer systems which, although still compatible with the original 80286-based AT.RTM. computer, are considered in some respects to be enhancements of it.
One manufacturer, Chips & Technologies, Inc. (C&T), 3050 Zanker Road, San Jose, Calif. 95134, has developed a chip set known as the NEAT.TM. chip set. The NEAT.TM. chip set is described in data sheets entitled "CS-8221 New Enhanced AT.RTM. (NEAT.TM. Data Book", (part/catalog no. 2-221-B 10M 3/88 Rev. 2, which, like all technical documents cited in this specification, is incorporated by reference as if reproduced in full below. See also C&T PRODUCT ALERT PA76.2/9-88, UPDATE--Sep. 21, 1988, "386SX/387SX BOARD DESIGN WITH NEAT AND CHIPS/250," and PA115/3-89, "UPDATE ON NEAT PLUS SX MODULE."
The C&T NEAT.TM. chip set has allowed development of AT.RTM.-compatible computer systems. Among the systems which are AT.RTM.-compatible is the 80286-based POWERFLEX.TM. system from Advanced Logic Research, Inc. (ALR.RTM.), 9401 Jeronimo, Irvine, Calif. 92718. As will be better appreciated by a reading of the Detailed Description of the Preferred Embodiments of the present invention (below), this computer system may advantageously be used in conjunction with the present invention.
There are several known methods of upgrading an AT.RTM.-compatible 80286-based computer systems.
A first upgrade method involves an "add-in card" which is inserted into the AT.RTM. bus, and in which a cable is extended form the add-in card to the CPU (central processor unit) socket on the system board. In a second upgrade method, a circuit board containing a higher performance CPU is inserted into the CPU socket. Both these methods involve the physical removal of the 80286 processor from its socket.
These known methods possess several disadvantages. The removal of a chip from the original processor board is not convenient for the user or customer. In fact, physical removal of the 80286 and insertion of the inter-card-connecting cable (or second board) into the original processor's socket may even cause physical or electronic damage, if not performed properly.
Furthermore, it is generally known that increased performance may be obtained through increasing CPU clock speed. These two methods, involving insertion of a cable or board into the CPU socket, do not provide for changing the clock speed. To change clock speeds using either of these two known methods, the crystal itself must be replaced. Replacement of a crystal is both inconvenient and dangerous to components.
Both of the above-described methods may decrease reliability due to introduction of unwanted signal noise into signals entering and leaving the CPU socket. Also, boards or cables plugged directly into the CPU socket may vibrate loose, causing intermittent connections.
A third upgrade method involves placement of an add-in board into the AT.RTM. slot, but in which the 80286 processor is not removed from the system board. The system powers up with the 80286 as the CPU. After powering up, however, system control is relinquished to the processor on the new board through what is commonly known as the "master mode". The master mode involves use of the DMA controller to request control of the external AT.RTM. bus, allowing the card to be "master" of the system.
This third method possesses the drawback that true AT.RTM. system compatibility is sacrificed. True compatibility cannot be maintained because the card is functioning on an external bus, and not directly on the CPU bus.
Therefore, there is a need in the computer industry for systems and methods for upgrading known computer systems which do not involve unnecessary cost, inconvenience for the user or customer, or introduction of features which are incompatible with any industry standards adhered to by the original computer system. Further, it is desirable to provide a system and method whereby a given computer system may be upgraded without the necessity of physically removing or replacing any portion of the original computer system, so as to minimize inconvenience and possibility of electronic or physical damage. It is further desirable to achieve these goals while maintaining compatibility with industry standards and maintaining system reliability.